CN109414961B

CN109414961B - Tyre comprising a tread comprising reinforcing elements

Info

Publication number: CN109414961B
Application number: CN201780041165.5A
Authority: CN
Inventors: F·佩林; P·帕洛; S·莫里瓦尔; C·卡雷姆
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2016-06-30
Filing date: 2017-06-23
Publication date: 2020-10-02
Anticipated expiration: 2037-06-23
Also published as: WO2018002488A1; US20190255887A1; EP3478518B1; CN109414961A; EP3478518A1; US11518194B2

Abstract

A tire having a tread comprising an undertread and a circumferential reinforcement composed of a rubber compound having a stiffness greater than the stiffness of the rubber compound and the undertread. The tire has an outer side and an inner side, and the circumferential reinforcement comprises tapered reinforcing elements in tread rib elements that are axially outside of and axially adjacent to the first or second circumferential groove of the tread when viewed from the outer side to the inner side.

Description

Tyre comprising a tread comprising reinforcing elements

Technical Field

The present invention relates to a tire, and more particularly to a tire having improved grip performance.

Background

It is known that, whether the tyre is intended to be mounted on a passenger or heavy vehicle, the tread of the tyre is provided with a tread pattern comprising, in particular, tread pattern elements or elementary blocks delimited by various main, longitudinal or circumferential, transverse or inclined grooves, said elementary blocks also being able to have various finer slits or grooves. The grooves form channels for the drainage of water during wet ground running, and the walls of these grooves define the leading and trailing edges of the tread pattern elements, depending on the direction of bending.

In order to improve the grip of the tire, and more particularly on dry and wet ground, it is known to reduce the stiffness (or rigidity or hardness) of the tread constituent rubber compounds. This reduction in tread stiffness results in a better matching of the tread to the rough surface of the running surface, and therefore an increase in the actual contact area with the running surface, and an improvement in grip performance relative to a tread that is harder with rubber compounds.

However, the use of a less rigid rubber tread compound promotes shearing of the tread pattern elements and their vibration, especially in the case of lateral grip, and this generates a greatly increased pressure on the leading edges of the tread pattern elements, which in turn generates a very significant amount of heat.

These elevated pressures and this heat can lead to very rapid damage to the tire tread and non-optimal utilization of the potential grip of the tread rubber compound.

In order to improve the performance of a tire having grooves by stabilizing the tread pattern elements, document EP 2708382 a1 proposes a tire having in its tread a circumferential reinforcement made of a rubber compound having a rigidity greater than that of the rubber compound of the rest of the tread, and the circumferential reinforcement elements being located below each circumferential groove and extending radially from the radially inner surface of the tread up to the entire bottom of the groove they form.

Another example is given in document JP H08342015.

The reinforcement of the circumferential groove thus produced makes it possible to increase the drift thrust of the tyre, but the presence of a rigid mixture in the bottom of the groove makes it difficult to mold the wear indicator. A significant increase in rolling resistance is also observed, particularly in relation to the limitation of the transverse and longitudinal flattening processes.

Disclosure of Invention

The subject of the invention is a tire having an axis of rotation and a median plane perpendicular to the axis of rotation and comprising a crown with a crown reinforcement, a tread situated radially on the outside, the tread comprising a plurality of tread pattern elements having lateral faces and contact faces intended to come into contact with the road surface when the tire is driven, a plurality of circumferential grooves, each of which is delimited by an outer face and an inner face of the opposite adjacent tread pattern element and by a bottom, a circumferential reinforcement made of a rubber compound having a rigidity greater than that of the rubber compound of the rest of the tread, and an underlayer arranged radially towards the inside and radially on the outside of the crown reinforcement, characterized in that the tire has an outer side and an inner side, the circumferential reinforcement having reinforcing elements, the reinforcing elements are provided in tread pattern elements arranged axially outside and axially adjacent to one of a first circumferential groove and a second circumferential groove of the tread from the outside to the inside, the reinforcing elements extending radially from the radially outer surface of the under layer toward the outside of the tread over part or all of the height of the tread thickness with a gradually decreasing axial width, the tread pattern elements arranged axially inside with respect to the first circumferential groove having no reinforcing elements provided adjacent to the axially inner face of the first circumferential groove, and the under layer having a stiffness less than or equal to the stiffness of the rubber compound of the circumferential reinforcing elements.

The circumferential reinforcing elements have, seen in meridian section, a corner shape with an inflection point oriented radially towards the outside, and are therefore provided at the trailing edge of the rib or on the trailing edge of the tread pattern element of the highest load outside the tread of the tire, during rapid cornering, opposing the shear and vibration of these tread pattern elements due to its high compression and shear stiffness, thus making it possible to maintain a large area of contact with the running surface to limit the bulging pressure on the leading edge of the rib or tread pattern element, and thus to limit the thermal and rapid wear of the leading edge of the rib. The presence of reinforcing elements and of a single groove of this structure has made it possible to obtain a significant improvement in the lateral grip performance of a vehicle tyre.

The circumferential reinforcing element also has the basic feature of bearing directly on the outer surface of the underlayer. A slight reduction in the axial shear stiffness of the ribs is observed compared to a direct support on the crown reinforcement of the tire, but a significant increase in the rolling resistance of the tire is associated with the greater ease of transverse and longitudinal flattening of the crown block of the tire.

It is very advantageous that the tread pattern elements axially disposed inside the first circumferential groove do not have reinforcing elements disposed close to the axially inner face of this groove. This is because, when these reinforcing elements are in contact with the running surface, the presence of these reinforcing elements on the leading edge of the second rib of the tread tends to cause deterioration of the grip properties of the tire and of the vehicle, due to the high rigidity of the material of these reinforcing elements.

It should also be noted that the reduction in volume of the very hard rubber results in a significant reduction in the rolling resistance of the tyre with respect to that disclosed in the above-mentioned document EP 2708382 a 1.

Preferably, the circumferential reinforcement has two reinforcing elements respectively arranged in tread pattern elements adjacent to the outer side and axially close to the first and second circumferential grooves of the tread from the outer side to the inner side.

This enhances the advantageous effect in terms of grip.

Advantageously, the tread has at least three circumferential grooves, the circumferential reinforcement also having a further reinforcing element arranged in the tread pattern element adjacent to and axially adjacent to a third circumferential groove of the tread from the outside to the inside.

The circumferential reinforcement may also advantageously have reinforcing elements arranged in all tread pattern elements adjacent to and axially close to the circumferential groove on the outer side.

According to one advantageous embodiment, the circumferential reinforcement has an inner reinforcing element arranged in the tread pattern element adjacent, on the inner side, to the circumferential groove axially closest to the inner side of the tyre.

This makes it possible to stabilize the ribs or tread pattern elements on the inside of the tire when this inside is loaded as a leading edge during cornering. Thus, the same anti-vibration and anti-shear effects associated with a high compression stiffness of the reinforcement element are found.

According to one advantageous exemplary embodiment, the tread has at least four circumferential grooves, the circumferential reinforcement having two inner reinforcing elements respectively arranged in tread pattern elements adjacent to and axially adjacent to the first and second circumferential grooves of the tread from the inner side to the outer side.

According to another advantageous embodiment, the circumferential reinforcing elements are arranged symmetrically with respect to the median plane of the tyre.

According to one particular exemplary embodiment, the tread has a circumferential groove crossed by the median plane, the two circumferential reinforcing elements being arranged axially close to and on either side of the circumferential groove crossed by the median plane.

The shape of the circumferential reinforcing element has a cross-section that tapers radially towards the outside. This increases its effectiveness as a support point. The wall of the circumferential reinforcing element may be concave, convex or in the form of a step.

Preferably, the angle of the two side walls of the circumferential reinforcing element is between 35 and 45 degrees.

Below 35 degrees the effectiveness of the bearing points is reduced, whereas above 45 degrees the volume of the circumferential reinforcing elements becomes too large.

According to a preferred embodiment, the reinforcing element has a base in radial contact with the outer surface of the underlayer and a top extending radially towards the outside for at least half the height of the side face of the adjacent circumferential groove.

This minimum height of the top of the circumferential reinforcing elements is useful for obtaining a stabilizing effect during the entire life of the tyre.

According to an advantageous embodiment, the tops of the reinforcing elements at least partially form the sides of adjacent circumferential grooves.

According to another advantageous embodiment, the tops of the reinforcing elements are arranged at an axial distance of 1 to 8mm, preferably 2 to 5mm, from the side of the adjacent circumferential groove.

This embodiment makes it possible to maintain the significant effect of improving the lateral grip performance of a vehicle tire without damaging the molding of the tread circumferential groove.

The base of the reinforcing element may advantageously extend axially below at least some of the bottoms of adjacent circumferential grooves.

This embodiment has the advantage of enhancing the effectiveness of the circumferential reinforcing elements.

According to another exemplary embodiment, the base of the reinforcing element extends axially below the tread pattern element on the side opposite the adjacent circumferential groove.

As previously mentioned, this has the advantage of stabilizing the circumferential reinforcing element.

According to another advantageous exemplary embodiment, the base of the reinforcing element may be axially continuous and extend axially over at least 50% of the axial width of the tyre tread.

Very advantageously, the base of the axially continuous reinforcing element extends axially over at most the axial width of the crown reinforcement. This makes it possible to maintain good flattening of the two shoulders of the tire and to limit the effect of the use of a very high stiffness rubber mixture on the rolling resistance of the tire.

Advantageously, the rubber mixture from which the circumferential reinforcement is made has a dynamic shear modulus G, measured at 60 ℃, 10Hz and an alternating shear stress of 0.7MPa, of greater than 20MPa, preferably greater than 30 MPa.

Very advantageously, the rubber mixture of the tread has a dynamic shear modulus G, measured at 60 ℃, 10Hz and an alternating shear stress of 0.7MPa, lower than or equal to 1.3MPa, preferably lower than 1.1 MPa.

The presence of the circumferential reinforcement makes it possible to exploit the grip capacity of such tread rubber compounds with very low stiffness. This is particularly useful in the case of tires for passenger vehicles.

According to an alternative embodiment, the underlayer is axially interrupted under at least one circumferential groove of the tread. This makes it possible to obtain axial shear stiffness without losing the ease of planarization of the rigid underlayer.

The invention relates more particularly to tyres intended to be fitted to motor vehicles having three or more wheels, motor vehicles of the passenger vehicle type, SUVs ("sport utility vehicles"), industrial vehicles such as those selected from vans, heavy vehicles (i.e. subways, buses, heavy road transport vehicles (trucks, tractors, trailers) or off-road vehicles), such as heavy agricultural vehicles or civil engineering vehicles, other transport or handling vehicles and two-wheeled vehicles (in particular motorcycles), or aircraft.

Drawings

The subject matter of the invention will now be described with the aid of the accompanying drawings, in which:

figure 1 very schematically shows (not drawn to any particular scale) a meridian cross section through a tyre according to one embodiment of the present invention;

figures 2 to 11 depict the tread in meridian cross section of a tyre according to different embodiments of the present invention; and

figure 12 shows an embodiment of the test tread in meridian cross section.

Detailed Description

Figure 1 schematically illustrates a radial cross-section of a pneumatic tire or tire containing circumferential reinforcement 20 according to one embodiment of the present invention.

The tire 1 has an outer side E intended to be positioned toward the vehicle outer side and an inner side I intended to be positioned toward the vehicle inner side. Thus, the tire exhibits tread asymmetry.

Fig. 1 also shows the axial X, circumferential C and radial Z directions and the median plane EP (the plane perpendicular to the axis of rotation of the tyre, which lies midway between the two beads 4 and passes through the middle of the crown reinforcement 6).

The tire 1 has a crown 2 reinforced with a crown reinforcement or belt 6, two sidewalls 3 and two beads 4, each of these beads 4 being reinforced with a bead wire 5. The crown reinforcement 6 is surmounted by a rubber tread 9 located radially on the outside. A rubber underlayer 15 is located between the crown reinforcement and the tread. A carcass reinforcement 7 is wound around the two bead wires 5 in each bead 4, the turn-up 8 of this reinforcement 7 being disposed, for example, towards the outside of the tyre 1. In a manner known per se, the carcass reinforcement 7 is constituted by at least one ply reinforced by so-called "radial" cords (for example textile or metal), i.e. these cords are arranged substantially parallel to each other and extend from one bead to the other so as to form an angle of between 80 ° and 90 ° with the median circumferential plane EP. The inner liner 10 extends radially from one bead to the other on the inner side with respect to the carcass reinforcement 7.

Depending on the purpose of the tire designer, the mixture of this underlayer 15 may have low hysteresis and low stiffness and thus improve the rolling resistance of the tire or be harder than the rubber mixture forming the tread 9; in the latter case, the under-layer has the effect of increasing the shear stiffness of the tire tread. However, the stiffness of this underlayer 15 is still less than the stiffness of the rubber compound of the circumferential reinforcement. In a particular embodiment, which simplifies the industrial production of the tire according to the invention, the rubber mixture of the underlayer and the constituent rubber mixture of the tread are identical.

The tread 9 has four

grooves

11, 12, 13 and 14 from the outer side E to the inner side I. Each groove has an outer face 11.1, 12.1, 13.1 and 14.1, a groove bottom 11.2, 12.2, 13.2 and 14.2 and an inner face 11.3, 12.3, 13.3 and 14.3.

The tread 9 also has a circumferential reinforcement 20, said circumferential reinforcement 20 being constituted by a reinforcing element 22 arranged adjacent to the outer wall 12.1 of the second groove 12. The reinforcing element 20 rests directly on the radially external wall of the bottom layer 15 and has a substantially triangular cross section. In the embodiment shown, the reinforcing element partially forms the outer wall 12.1 of the groove 12.

The circumferential reinforcement 20 opposes the vibration and shearing of the ribs adjacent to the outside of the groove 12 when the tire is subjected to a high lateral load, which is oriented axially from the outside to the inside, for example, during cornering of the vehicle on which the tire is mounted in the direction of the inside of the tire.

Fig. 2 to 10 depict radial cross sections of a tread according to different embodiments of the invention in the case of a tread pattern with three circumferential grooves.

The tread 30 in fig. 2 has three

grooves

11, 12 and 13 and a circumferential reinforcement 32 comprising two

circumferential reinforcing elements

34 and 36. The circumferential reinforcing element 34 is arranged as in fig. 1 adjacent to the outer wall 12.1 of the second groove 12. The circumferential reinforcing element 34 rests against the radially outer wall of the bottom layer 15 and partially forms the outer wall 12.1 of the groove 12.

The additional circumferential reinforcing element 36 is arranged adjacent to the outer wall 11.1 of the first groove 11. By the presence of the additional circumferential reinforcing elements 36, they oppose the shearing and vibrations of the tread pattern elements adjacent to the outside of the first grooves 11, thus cooperating with the action of the circumferential reinforcing elements 34 when the tyre is subjected to high transverse loads. The tread has a rubber underlayer 15, which is in direct contact, on one side, with the outer surface of the crown reinforcement 6 and, on the other side, with the tread 9 and with the base of the reinforcing

elements

34 and 36.

The circumferential reinforcement 42 of the tread 40 in fig. 3 comprises three

circumferential reinforcing elements

44, 46 and 48. An additional circumferential reinforcing element 48, with respect to the circumferential reinforcement 32 of fig. 2, is arranged adjacent to the outer wall 13.1 of the third groove. The three circumferential reinforcing elements of the tread 40 cooperate to oppose vibration and shear of the tread pattern elements adjacent the exterior of the three grooves when the lateral load directed from the outside to the inside is strong. As mentioned above, a rubber underlayer 15 is provided between the crown reinforcement 6 and the tread 9 and the three circumferential reinforcing elements.

Fig. 4 shows an embodiment of a tread 50 according to one subject of the invention, in which, as shown in fig. 3, the circumferential reinforcement 52 comprises three

elements

54, 56 and 58 and an additional circumferential reinforcing element 59. The circumferential reinforcing element 59 is arranged adjacent to the inner wall 13.3 of the groove 13. This circumferential reinforcing element 59 opposes the vibrations and shearing of the tread pattern elements adjacent to the inside of the third groove 13 during the orientation of the transverse load from the inside to the outside. In this case, the load oriented from the inside to the outside is significantly weaker than the load oriented in the other direction in view of the dynamics of the vehicle when turning, and it is not necessary to add an additional circumferential reinforcing element. In the bending at the time of the limit of grip, the tire on the vehicle disposed in the bending is largely unloaded in consideration of the dynamics of the vehicle when turning. However, the tire located on the inside of the bend contributes to the lateral grip by its facing towards the front shoulder of the vehicle. The presence of reinforcements on the asymmetric tyre makes it possible to increase the total thrust on the shaft, due to the thrust of the two tyres on the same shaft. The bases of the four circumferential reinforcing elements bear directly on the radially outer surface of the underlayer 15.

In fig. 5, the tread 60 comprises a circumferential reinforcement 62, the circumferential reinforcement 62 being constituted by four

circumferential reinforcing elements

64, 66, 68 and 69 arranged in a manner similar to that of fig. 4. The four circumferential reinforcing elements have a base 61 and a top 63. In the embodiment shown, the base 61, which is in direct contact with the outer surface of the bottom layer 15, extends below the rib or tread pattern element adjacent to the three grooves. These extensions enhance the reinforcement provided by the different circumferential reinforcing elements.

In fig. 6, the tread 70 comprises a circumferential reinforcement 72, which, as shown in fig. 5, is constituted by four

circumferential reinforcing elements

74, 76, 78 and 79. These circumferential reinforcing elements have a top 73 and a base 71 and have their bases 71 extending below the adjacent grooves. As previously described, the base is in direct contact with the sub-layer 15 and reinforces the reinforcement provided by the various circumferential reinforcing elements. The radial height of the base 71 is substantially equal to the radial position of the groove bottom, so that they form the bottom of the rib. According to an alternative embodiment, the bottom of the rib is formed solely by the mixture of the tread.

In fig. 7, the tread 80 has a circumferential reinforcement 82, the circumferential reinforcement 82 being constituted by four

circumferential reinforcing elements

84, 86, 88 and 89, such that its base 81 is axially continuous and extends continuously from one side of the tread to the other. The base 81 is therefore in continuous direct contact with the radially external surface of the rubber underlayer 15 and has the significant function of reinforcing the entire crown 2 of the tyre. The top 83 of the reinforcing element partially forms the side of the adjacent rib.

The axially continuous base 81 has an axial width that covers at least half the axial width of the tread and at most the axial width W of the crown reinforcement 6. The fact that the base is continuous enhances the resistance of the entire crown block 2 to vibrations during transverse loads and that they do not exceed the axial width of the crown reinforcement 6 promotes the flattening of the shoulders and limits the rolling resistance of the tire.

The shape of the depicted circumferential reinforcing elements is triangular, but in particular the shape may vary without departing from the scope of the invention, and the side walls may be concave, convex or in the form of steps.

In the depicted embodiment, the angle α formed by the two sidewalls is about 40 degrees, i.e., between 35 and 45 degrees.

When the tire is new, the radial height of the circumferential reinforcing elements may reach the contact surface of the tread pattern elements, but may also be smaller. It should not be less than half the height of the tread pattern elements in order to be able to function during the entire life of the tire.

Fig. 8 depicts a tread 90, the circumferential reinforcement 92 of said tread 90 consisting of four

circumferential reinforcing elements

94, 96, 98 and 99 as shown in fig. 4. Four circumferential reinforcing elements bear against the radially outer surface of the rubber bottom layer 95. However, in this exemplary embodiment, the floor 95 is axially interrupted below the bottom of the

grooves

11, 12 and 13. Thus, the bottom layer 95 is comprised of four circumferential strips. When the rigidity of the under layer 95 is greater than that of the tread, this embodiment has an advantage of not restricting the lateral flattening.

The circumferential reinforcing elements should serve as bearing points for resisting shear and vibration of the tread pattern elements containing them. For this purpose, the mixture from which these circumferential reinforcing elements are made is preferably very substantially harder than the mixture of the tread 9. Preferably, the dynamic shear modulus G measured at 60 ℃, 10Hz and 0.7MPa alternating shear stress is greater than 20MPa, very preferably greater than 30 MPa.

Such a mixture is described in particular in the applicant's application WO 2011/045342 a 1.

An example of such a formulation is given in Table 1 below

TABLE 1

Components	C.1
		NR(1)	100
Carbon black (2)	70
		Phenol-formaldehyde resin (3)	12
ZnO(4)	3
		Stearic acid (5)	2
6PPD(6)	2.5
		HMT(7)	4
Sulfur	3
		CBS(8)	2

(1) Natural rubber;

(2) carbon black N326 (named according to standard ASTM D-1765); (3) phenol-formaldehyde novolak resin ("Peracit 4536K" from Perstorp);

(4) zinc oxide (technical-Umicore);

(5) stearin ("Pristerene 4931" from Uniqema);

(6) n- (1, 3-dimethylbutyl) -N-phenyl-p-phenylenediamine (Santoflex 6-PPD from Flexsys);

(7) hexamethylenetetramine (from Degussa);

(8) N-Cyclohexylphenylthiazolesulfanimide (Santocure CBS from Flexsys).

The formulation makes it possible to obtain a mixture of high rigidity, in particular by the combined action of the epoxy resin and of the amine-containing curing agent. The shear modulus G measured at 0.7MPa alternating shear stress, 10Hz and 60 ℃ was 30.3 MPa.

Such a very hard material for the circumferential reinforcement is preferably used for a tread of low stiffness, with a dynamic modulus G of less than 1.3MPa and preferably less than or equal to 1.1 MPa.

One example of a suitable formulation is given in table 2 below:

TABLE 2

Composition comprising a metal oxide and a metal oxide	B1
		SBR(a)	100
Silicon dioxide (b)	110
		Coupling agent (c)	9
Liquid plasticizer (d)	20
		Resin plasticizer (e)	50
Carbon black	5
		Zinc oxide	3
Stearic acid	2
		Antioxidant (f)	2
Accelerator (g)	2
		DPG	2
Sulfur	1

The formulations are given by weight.

(a) SBR having 27% styrene, 5% 1, 2-butadiene, 15% cis-1, 4: 15%, trans-1, 4: 80% Tg-48 ℃;

(b) silica "Zeosil 1165 MP" from Solvay having a BET surface area of 160m²/g；

(c) "SI 69" TESPT silane from Evonik;

(d) "Flexon 630" TDAE oil from Shell;

(e) "Escorez 2173" resin from Exxon;

(f) antioxidant from Solutia "Santoflex 6 PPD";

(g) accelerator "Santocure CBS" from Solutia.

The dynamic shear modulus after vulcanization was 0.9 MPa.

Fig. 9 depicts a tread 100 having a circumferential reinforcement 102, said circumferential reinforcement 102 having three

circumferential reinforcing elements

104, 106 and 108 arranged as in fig. 3, said three

circumferential reinforcing elements

104, 106 and 108 bearing directly on the underlayer 15, close to the three grooves and on the outside. However, in this embodiment, the inner side walls of the crests 103 of the three circumferential reinforcing elements do not form part of the outer surface of the ribs, but are axially offset towards the outside so as to be spaced from the outer surface of these ribs by a distance of 1 to 8mm, preferably 2 to 5 mm. This offset makes it possible to not break the moulding of the rib during the vulcanisation of the tyre without reducing the effectiveness of the circumferential reinforcing elements.

In this fig. 9, it can also be seen that the tops of the circumferential reinforcing elements 104 extend radially up to the outer surface of the tread pattern elements. This makes the static charge easier to be discharged due to the conductive nature of the mixture of circumferential reinforcing elements.

Fig. 10 and 11 depict another embodiment of a tire according to the inventive subject matter, wherein the circumferential reinforcements are symmetrically disposed in the tread.

The tread 120 of fig. 10 has three

grooves

11, 12 and 13 and a circumferential reinforcement 122. In this embodiment according to one subject of the invention, the circumferential reinforcement 122 comprises four

circumferential reinforcing elements

124, 126, 128 and 129, said four

circumferential reinforcing elements

124, 126, 128 and 129 being arranged symmetrically with respect to the median plane EP and bearing directly on the surface of the underlayer 15. The arrangement of the three

circumferential reinforcing elements

124, 126 and 128 is similar to the reinforcing

elements

54, 56 and 59 in fig. 4. In contrast, the reinforcing element 129 is arranged axially on the inside with respect to the groove 12, thus forming at least a part of the inner surface 12.3 of the groove. Thus, the circumferential reinforcement 122 does not add any asymmetry to the tread 120, making installation easier when such a tire does not have any other asymmetry. The outer side of such a tire can therefore be mounted towards the outside or the inside of the vehicle, these inside and outside being only geometric references in this case.

Fig. 11 depicts a tread 130 having four

grooves

11, 12, 13, 14 and circumferential reinforcement 132. The circumferential reinforcement 132 has four

circumferential reinforcement elements

134, 136, 138 and 139 that rest against the surface of the sub-layer 15. In the embodiment of fig. 12, the four circumferential reinforcing elements are arranged symmetrically with respect to the median plane EP of the tyre. The reinforcing

elements

134 and 136 are arranged axially outside the

grooves

12 and 11, respectively; reinforcing

elements

138 and 139 are arranged axially inside the

grooves

14 and 13, respectively.

In particular for asymmetric or symmetric tires, the person skilled in the art as tire designer should be able to adjust the number and position of the circumferential reinforcing elements so as to obtain an optimal resistance to vibrations and shearing of the ribs and tread pattern elements.

Testing

The rubber mixtures were characterized as follows.

Dynamic characteristics are well known to those skilled in the art. These properties were measured on a viscosity analyzer (Metravib VA4000) using test specimens molded from the unvulcanized mixture or bonded together with the vulcanized mixture. The test samples used were those depicted in figure X2.1 (circular ring test sample) in standard ASTM D5992-96 (using the version published on month 9 2006, first passed in 1996). The diameter "d" of the test specimen was 10mm (hence the circular cross-section was 78.5 mm)²) The thickness "L" of each portion of the mixture is 2mm, giving a ratio "d/L" of 5 (contrary to the standard ISO 2856, which is mentioned at paragraph X2.4 of the ASTM standard, the recommended value d/L is 2).

The response of samples of the vulcanized composition to a simple alternating sinusoidal shear stress at a frequency of 10Hz was recorded. The maximum applied shear stress was 0.7 MPa.

The measurements were carried out at a minimum temperature below the glass transition temperature (Tg) of the mixture or rubber to a maximum temperature above 100 ℃ with a temperature variation of 1.5 ℃ per minute. The test samples were conditioned for 20 minutes at the lowest temperature before the test began to ensure good temperature uniformity in the test samples.

The results used are in particular the values of the dynamic shear modulus G at a temperature of 60 ℃.

The performance of the tyre according to the subject of the invention was measured during the following tests:

-longitudinal braking distance: the distance required on wet ground to reach 20km/h from 80km/h was measured.

-steering stiffness: for a given drift angle, the axial transverse thrust of the tire is measured during rolling.

Speed test on Charade loop: the test consisted of four cycles and the selected performance was the average of four times. The control tires were used at the beginning and end of the test to enable correction of possible drifts associated with, for example, changes in air temperature and ground temperature conditions.

Test of

Fig. 12 very schematically depicts a cross section of a tread of a tire for vehicle testing.

The tread 110 has four

grooves

11, 12, 13 and 14. The two mixtures constitute the tread, the mixture 113 being radially on the outside of the underlayer 115. The tread 110 also has a circumferential reinforcement 112 comprising five

circumferential reinforcing elements

114, 116, 117, 118 and 119 radially abutting directly against the outer surface of the underlayer 115.

Circumferential reinforcing elements

114, 116 and 118 are each disposed adjacent to the outer surface of one of the three outermost ribs. The

circumferential reinforcing elements

119 and 120 are themselves arranged adjacent to the inner surface of one of the two ribs arranged closest to the inside. Thus, the third rib is reinforced by two circumferential reinforcing elements. Each circumferential reinforcing element has a substantially triangular shape and is intended to be in direct contact with the radially outer surface of the rubber under-layer 115 and one of its side walls partially forms the side of the rib.

The tread 110 of the test tire is produced by means of a profile having two mixtures, made into a tread 113 and a base layer 115, obtained by coextrusion. The profile has four grooves. Profiles of the same length corresponding to four circumferential reinforcing elements are also produced by extrusion. Then, four volumes of mixture, each corresponding to the volume and shape of the circumferential reinforcing elements, were removed from the co-extruded profile of the two tread mixtures with the heated chisel, and then the four circumferential reinforcing elements were manually placed in the four volumes thus obtained. The tread thus assembled is then placed over the crown of the tire to complete it in a manner well known to those skilled in the art. The completed tire is then cured as usual in a curing press.

The reference tire was a michelin tire of Pilot Sport type 3, size 225/45R17, front pressure 2.3 bar, rear pressure 2.7 bar, and test vehicle was of Renault ciio Cup type.

These reference tires R1 had treads whose mixture had a dynamic shear modulus G at 60 ℃ of 1.4 MPa.

Other reference tires R2 were also produced. The tread of these tires is the same as that of fig. 12, except that there are no four circumferential reinforcing elements and no underlayer. These tires have a tread pattern formed only by the four circumferential grooves shown.

The G value of the tread mixture of reference tire R2 at 60 ℃ was 0.9 MPa.

Test tyre E1 had a tread mixture with a G value of 0.9MPa and the circumferential reinforcing elements were made of a mixture with a G value of 30 MPa. These tires E1 have circumferential reinforcements corresponding to fig. 10, but no underlayer.

Other tires according to the invention were manufactured E2 with a tread and a circumferential reinforcement like E1, but additionally with an underlayer. Preferably, the mixture from which the underlayer is made has a dynamic shear modulus G, measured at 60 ℃, 10Hz and an alternating shear stress of 0.7MPa, of less than 20MPa, preferably less than 10 MPa. In tire E2, the dynamic shear modulus G of the underlayer mixture is equal to 5 MPa. The bottom layer is continuous as shown in fig. 12. The thickness of this underlayer is about 2mm in the tread pattern.

The circumferential reinforcing elements have an angle of 40 degrees between their side walls.

TABLE 3

The use of a lower stiffness tread generally reduces the steering stiffness of the tire and improves braking performance on wet ground.

The tire tested according to the invention makes it possible to obtain a braking performance gain of 10 points on wet ground, while having a steering stiffness comparable to that of the control R1.

TABLE 4

	Time of day	Time gain
			R1	2min 18s	-
R2	2min 17.7	0.3s
			E1	2min 17.2	0.8s
E2	2min 17.0	1.0s

The gain from 0.3s on the track is considered significant.

It can be seen that the use of a tread with a mixture having a very low stiffness gives only a barely significant gain, while the results obtained with the tire with circumferential reinforcement according to the invention are very significant.

The presence of circumferential reinforcements in the tread thus makes it possible to exploit the potential grip of the tread mixture of lower stiffness.

By combining the selection of tread mix, the selection of mix of underlayer and circumferential reinforcement, the tire designer can compensate for the trade-off between grip and behavior and rolling resistance, respectively, which cannot be achieved by selecting a single tread material.

Claims

1. Tyre (1) having an axis of rotation and a median plane (EP) perpendicular to the axis of rotation, and comprising a crown having:

a crown reinforcement (6); and

a tread (9, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130) located radially on the outside, the tread comprising:

a plurality of tread pattern elements having lateral faces (11.1, 11.3, 12.1, 12.3, 13.1, 13.3, 14.1, 14.3) and a contact face intended to be in contact with the road surface when the tyre is driven;

a plurality of circumferential grooves (11, 12, 13, 14), each circumferential groove being delimited by an outer side (11.1, 12.1, 13.1, 14.1) and an inner side (11.3, 12.3, 13.3, 14.3) of opposite adjacent tread pattern elements, and by a bottom (11.2, 12.2, 13.2, 14.2);

o circumferential reinforcement (20, 32, 42, 52, 62, 72, 82, 92, 102, 112, 122, 132) made of a rubber compound having a stiffness greater than that of the rubber compound of the rest of the tread; and

an underlayer (15, 95, 115) arranged radially towards the inside and radially outside the crown reinforcement;

characterized in that the tyre has an outer side (E) and an inner side (I), the circumferential reinforcement having reinforcing elements (22, 34, 36, 44, 46, 54, 56, 64, 66, 74, 76, 84, 86, 94, 96, 104, 106, 114, 116, 124, 126, 134, 136) provided in tread pattern elements arranged axially on the outer side with respect to one of a first and a second circumferential groove of the tread from the outer side to the inner side and axially close to said circumferential groove, the reinforcing elements extending radially from the radially outer surface of the underlayer towards the outer side of the tread over part or all of the height of the tread thickness with a progressively decreasing axial width, the tread pattern elements arranged axially on the inner side with respect to the first circumferential groove (11) not having reinforcing elements provided close to the axially inner face of the first circumferential groove, and the stiffness of the bottom layer is less than or equal to the stiffness of the rubber compound of the circumferential reinforcement.

2. Tyre according to claim 1, wherein the circumferential reinforcement (32, 42, 52, 62, 72, 82, 92, 102, 112, 122, 132) has two reinforcing elements respectively provided in tread pattern elements adjacent to the outer side in a first circumferential groove (11) and a second circumferential groove (12) from the outer side to the inner side of the tread and axially adjacent to said first circumferential groove (11) and second circumferential groove (12).

3. Tyre according to claim 1, wherein said tread has at least three circumferential grooves (11, 12, 13), the circumferential reinforcement (42, 52, 62, 72, 82, 92, 102, 112) further having another reinforcing element provided in a tread pattern element adjacent to and axially adjacent to a third circumferential groove (13) of the tread from the outside to the inside.

4. Tyre according to claim 1, wherein the circumferential reinforcement (42, 52, 62, 72, 82, 92, 102) has reinforcing elements provided in all tread pattern elements adjacent to and axially close to the circumferential groove on the outer side.

5. Tyre according to claim 1, wherein the circumferential reinforcement (52, 62, 72, 82, 92, 112, 122, 132) further has an inner reinforcing element provided in the tread pattern element adjacent, on the inner side, to the circumferential groove axially closest to the inner side of the tyre.

6. Tyre according to claim 5, wherein the tread (110, 130) has at least four circumferential grooves, the circumferential reinforcement (112, 132) having two inner reinforcing elements respectively provided in tread pattern elements adjacent to and axially adjacent to the first and second circumferential grooves of the tread from the inner side to the outer side.

7. Tyre according to claim 1, wherein the circumferential reinforcing elements (124, 126, 128, 129, 134, 136, 138, 139) of the circumferential reinforcement (122, 132) are arranged symmetrically with respect to said median plane.

8. Tyre according to claim 7, wherein the tread has a circumferential groove crossed by a median plane, the two circumferential reinforcing elements (124, 129) being arranged axially close to and on either side of said circumferential groove crossed by said median plane.

9. Tyre according to claim 1, wherein the angle of the two sidewalls of the reinforcing element is between 35 and 45 degrees.

10. Tyre according to claim 1, wherein the reinforcing elements have a base (61, 71, 81) and a top (63, 73, 83, 103) radially arranged on the outer surface of the underlayer, said top extending radially towards the outside for at least half the height of the side of the adjacent circumferential groove.